The Lost Trophy Game

11 years ago, a party of an alien race landed on our colonial planet. There were five of them in total. Soon after they established some sort of base, they started to terrorize the area. They killed people for fun and burnt down villages. The colony was on the verge of destruction. It seemes we'd lost it to them, but then a hero appeared. A vigilante, Eugene Stormer. He hunted them down, one by one. He was very cautious and stategic and took his time. In two months he got rid of them. He made a trophy out of the leader's skull. That trophy now worths millions. Although, after Stormer's mysterious death, it went missing and a great pursuit of the lost trophy had started.